Gas-blast circuit breaker having a movable tubular venting contact and a laterally arranged exhaust vent in the interrupting chamber



April 1968 R. G. COLCLASER, JR. ETAL 3,379,348

GAS-BLAST CIRCUIT BREAKER HAVING A MOVABLE TUBULAR VENTING CONTACT AND A LATERALLY ARRANGED EXHAUST VENT IN THE INTERRUPTING CHAMBER Filed Jan. 26, 1965 4 Sheets-Sheet 1 l w h u. ul

WITNESSES INVENTORS ATTORNEY April 1968 R. e. COLCLASER, JR.. ETAL 3,379.848

GAS-BLAST CIRCUIT BREAKER HAVING A MOVABLE TUBULAR VENTING CONTACT AND A LATERALLY ARRANGED EXHAUST VENT IN THE INTERRUPTING CHAMBER Filed Jan. 26, 1965 4 Sheets-Sheet 2 3 m wE x mm 8 fiw O 5 5. 0 a mm Nm 8 mm mm rvm l/l I/OU N/ a n I M, 8 5 mm 5 3 a mw HU A 3 mm qm f 8 m mm vv 9. wmnwmwmm U Lfw i; 1 E5 1 A 1 3. N m

April 23, 1968 R. G. COLCLASER. JR. ETAL ,8 8

GAS-BLAST CIRCUIT BREAKER HAVING A MOVABLE TUBULAR VENTING CONTACT AND A LATERALLY ARRANGED EXHAUST VENT IN THE INTERRUPTING CHAMBER 4 Sheets-Sh 1 46' III Filed Jan. 26, 1965 FIG. 3.

FIG. ll.

FIG. I2.

FIG. 9

7 I 7 B e F Aprll 1968 R. G. COLCLASER, JR.. ETAL 3,379.848

GAS-BLAST CIRCUIT BREAKER HAVING A MOVABLE TUBULAR VENTING CONTACT AND A LATERALLY ARRANGED EXHAUST VENT IN THE INTERRUPTING CHAMBER Filed Jan. 26, 1965 4 Sheets-Sheet FIG. l4.

United States Patent 0 GAS-BLAST ClRCUIT BREAKER HAVING A MUV- ABLE TUBULAR VENTHNG @GNTACT AND A LATERALLY ARRANGED EXHAUST VENT IN THE KNTERRUPTENG CHAMBER Robert G. Coiclascr, lira, Franklin Township, Belmont, and Frank L. Reese, Wilkinslaurg, Pa, assignors to Westinghouse Electric Corporation, East Pittsburgh, Pin, a corporation of Pennsylvania Filed Jan. 26, 1965, Ser. No. 428,077 3 Claims. (Cl. 260-448) ABSTRACT 0F THE DISCLOSURE A gas-blast circuit breaker has a fixed arcing chamber enclosing a stationary contact structure and having an orifice opening leading therefrom together with a laterally arranged exhaust vent. A movable tubular venting contact cooperates with the stationary contact structure to establish an arc, and the gas flow carries the arc interiorly of the movable tubular venting contact. The provision of a laterally arranged exhaust vent provides an additional transverse cross-blasting action of the gas across the established are for additional arc extinguishing effectiveness.

This invention relates, generally, to circuit breakers and, more particularly, to circuit breakers having interrupting units of the gas-blast type.

Prior-art circuit breakers of the dual-pressure gas-blast type have interrupting units of the axial-flow type, in which gas flows through a generally tubular moving contact member in an axial direction to interrupt the are drawn between the moving contact and the fixed contact of the circuit breaker. Reference may be had to United States patent application filed Oct. 7, 1960, Ser. No. 61,284, now US. Patent 3,154,658, issued Oct. 27, 1964, to Robert G. Colclaser, In, and Russell N. Yeckley, in this connection. Tests have demonstrated that under high rates of rise of recovery-voltage conditions, better interrupting performance can be obtained by utilizing a crossblast interrupter instead of an axial flow interrupter. However, certain features of the axial-flow structure are desirable when interrupting high-voltage circuits.

An object of this invention is to provide an improved cross-blast type of interrupting unit in a circuit breaker.

A further object of the invention is to provide a circuit breaker having a plurality of cross-blast type interrupting units connected in series.

Another object of the invention is to provide a simplified and improved contact finger and arc-horn structure for the contact structure of a circuit interrupter.

A still further object of the invention is to provide an improved cross-blast circuit interrupter having a maximum fixed arc gap.

Still another object of the invention is to utilize one blast valve for controlling the flow of gas directed toward a plurality of interrupters of the cross-blast type.

Another object is to provide an improved interrupting unit in which additional interrupting effort is supplied by a lateral exhaust vent, so as to create a cross-blast action, in addition to other directed gas flow.

A further object of the invention is to provide an improved gas-blast interrupting unit in which a combination axial-flow and cross-blast flow is achieved.

Yet a further object of the invention is to provide an improved interrupting unit having a vented tubular movable contact through which exhaust flow is generated, and, additionally, in which a transverse cross-blast flow action is obtained by the provision of a lateral exhaust vent for the associated interrupting chamber.

Other objects of the invention will be explained fully hereinafter, or will be apparent to those skilled in the art.

In accordance with one embodiment of the invention, a generally cylindrical horizontally extending grounded metal tank contains a generally cylindrical contact member which is engaged by a generally cylindrical cluster of finger contact members and is moved axially to open the circuit through the contact members. A support member having a passageway therethrough connects a highpressure reservoir to an interrupting chamber. Highpressure gas released from the reservoir by a blast valve flows to the interrupting chamber where a cross-blast is formed to interrupt the arc drawn between the contact members. An arc-horn is mounted outside the cluster of contact fingers adjacent an exhaust vent in the interrupting chamber, so that the arc is blown against a rib across the vent which acts as an arc splitter to lengthen the arc. The high-pressure reservoir is located at one end of the tank, and one blast valve controls the flow of gas to a plurality of cross-blast interrupters disposed axially along the tank.

In accordance with a further embodiment of the invention, there is provided an improved cross-blast type of interrupting unit in which a movable tubular vented contact is withdrawn out of an orifice opening provided in the interrupting chamber and in which, additionally, a lateral exhaust vent is supplied to provide a transverse blast of gas in addition to the axial flow of gas through the vented movable tubular contact. A further embodiment of the invention includes the provision of an interrupting chamber having a contact orifice opening, through which the movable contact is withdrawn, and also having a lateral exhaust vent which cooperates with the incoming gas flow to create a transverse cross-blast interrupting action.

For a better understanding of the nature and objects of the invention, reference may be had to the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a View, in perspective, of a three-pole circuit breaker embodying principal features of the invention;

FIG. 2 is a view, partly in elevation and partly in section, of one pole-unit of the circuit breaker;

FIG. 3 is a view, partly in elevation and partly in section, of the first-break interrupting unit of one poleunit of the circuit breaker, the contact members being closed;

RIG. 4 is a detail view looking in the direction of the arrows IVIV in FIG. 3;

FIG. 5 is a view, similar to FIG. 3, the contact memhere being partly open, and additionally taken along the line V-V of FIG. 6;

FIG. 6 is a view, partly in section and partly in end elevation, of the interrupting chamber of FIG. 3 taken along the line VI-VI of FIG. 5;

FIG. 7 is a view, similar to FIG. 3, of the secondbreak interrupter unit of the pole-unit of FIG. 2;

FIGS. 8, 9 and 10 are views, similar to FIGS. 3, 4 and 6, respectively, of a modified-type interrupting unit;

FIG. 11 is a view, similar to FIG. 5, of another modification of the interrupting unit;

FIG. 12 is a detail side elevational view of an intermediate contact finger assembly for the interrupter unit of FIG. 11;

FIG. 13 is a detail view, looking in the direction of the arrows XIII-XIII of FIG. 11;

FIG. 14 is a fragmentary vertical cross-sectional view taken through the interrupting unit of FIGS. 3 and 5 illustrating additional axial blasting action in combination with the cross-blast transverse fiow, the contact structure being illustrated in the partially open-circuit position; and

FIG. 15 is a fragmentary vertical sectional view taken through a modified-type of interrupting unit having a movable tubular vented "contact, in which axial gas flow occurs in addition to a transverse cross-blast action, the contact structure being illustrated in the partially opencircuit position.

Referring to the drawings, and more particularly to Each tank 2 has two cylindrical portions 6, which extend upwardly at opposite ends of the tank. A terminal bushing 7 is mounted on top of each cylindrical portion 6 with a lower end portion 8 of the terminal bushing extending into the interior of the tank 2, as shown in FIG. 2. The lower ends 8 of the terminal bushings 7 support the arc-extinguishing assembly 4, which bridges the terminal bushings 7.

Each tank 2 contains an interupting gas, such as, for example, sulfur hexafiouride (SF gas, at a relatively low pressure, such as 45 p.s.i.g. Other known gases, or

mixtures of gases, may, however, be utilized, if desired. A high-pressure reservoir 9 is mounted inside each tank 2 at one end of the assemblage 4. The reservoir 9 contains the same kind of an interrupting gas at a relatively high pressure, for example 200 p.s.i.g. An auxiliary, or

reserve high-pressure reservoir 11 is mounted below each tank 2, as shown in FIG. 1. A supply pipe line 12 and an insulating tube 12a connect each auxiliary reservoir 11 with its respective reservoir 9 inside the tank 2.

As shown in FIG. 1, a mechanism housing 13 is pro- L,

vided at one end of the supporting framework 5. The housing 13 encloses gas-control equipment and a compressor (not shown), which extracts relatively low-pressure gas from the interior of the several tanks 2, compresses the gas, and then forces it into the high-pressure reservoirs 9 and 11. Sufficient gas is stored in the high-pressure reservoirs 9, 11 for several interrupting operations without requiring operation of the compressor.

The housing 13 also contains a suitable operating mechanism, for example one of the pneumatic type, which 1 provides reciprocal motion of an operating shaft disposed inside of a tube 14, which interconnects the three poleunits A, B and C. The operating shaft, not shown, is connected to an operating crank-arm 15 (FIG. 2) in each one of the tanks 2.

As shown most clearly in FIG. 2, the arc-extinguishing assembly 4 includes two spaced insulating support bars 18 having their ends attached to support casting members 21 and 22 by bolts 19. The support members 21 and 22 are attached to the lower ends 8 of the terminal bushings 7. The high-pressure reservoir 9 is also attached to the support'member 22. Intermediate support members 22 of the arc-extinguishing assembly 4 are attached to the support bars 18 by bolts 20.

As shown most clearly in FIG. 3, the support member 22 has a passageway 23 therethrough, which connects with the interior of the high-pressure reservoir 9. A blast valve 24 controls the flow of gas from the reservoir 9 into the passageway 23. The blast valve 24 is biased to the closed position by spring 25, and is opened by a pivoted lever 26, which is actuated by a ratchet pawl 27. The pawl 27 is driven by a main operating lever casting 28, which is pivoted on a stationary pivot shaft 29. The pawl 27 is connected to the lever 28 through a suitable linkage mechanism (not shown). Reference may be had 4 to United States patent application filed Oct. 17, 1960, Ser. No. 63,201, now U.S. Patent 3,164,704, issued Jan. 5, 1965, to Russell N. Yecldey, Joseph Sucha and Roswell G. V an Sickle, in this connection.

The operating lever casting 28 is connected to the crank-arm by an insulating connecting rod 30. The main operating lever casting 28 also has a pair of thrust links 31 (only one being shown in FIG. 2) pivotally attached thereto, as at 32. The left-hand ends of the thrust links 31 are pivotally connected to the right-hand ends of two spaced movable operating rods 33, which move in a reciprocal manner during the opening and closing operations of the circuit interrupter 1,

The left-hand ends of the two spaced insulating operating rods 33 are connected by a bridging spring plate 34, which is biased toward the left by a compression spring 35. The spring 35 is compressed when the contact members of the circuit interrupter 1 are closed. When the operating mechanism for the circuit breaker is released by the tripping mechanism, the connecting rod is permitted to move toward the right, thereby allowing the accelerating spring to drive the operating rods 33 to the left to thereby open the movable contact members of the interrupter. The spring plate 34 strikes a bumper stop 36 at the end of the opening operation, thereby bringing the entire moving contact assembly 16 to a cushioned stop.

The two operating rods 33 of the movable contact assembly 16 are also interconnected by a plurality of cross-arms 37, which are spaced axially along the rods 33 as shown in FIG. 2. The cross-arms 37 are pivotally attached to the operating rods 33 and form a generally ladder-like structure, which is reciprocated by the main operating lever 28 and the spring 35 in the manner hereinbefore described.

As shown in FIGS. 2 and 3, an interrupting chamber or unit 41 is attached to the support member 22. Similar interrupting chambers, or units 41 are attached to two additional support members 22 spaced longitudinally inside the tank 2. Thus, three interrupting breaks are provided to interrupt the circuit extending between the two terminal bushings 7 of each pole-unit of the circuit breaker. In this manner, the breaker is made suitable for use on relatively high-voltage circuits.

The interrupting chambers 41 are preferably composed of a suitable high-temperature material, such as polytetrafluoroethylene. As shown in FIG. 3, the interrupting chamber 41 has an intake opening 42 and an exhaust vent 43 opposite the intake opening 42. The intake opening 42 communicates with the passageway 23 through a blast tube portion 44, which may be formed integrally with the chamber 41, as shown in FIG. 3, or, as shown in FIG. 8, may be a relatively short separate tube 44'. A rib, or splitter member 45 may be provided across the vent opening 43.

As shown in FIGS. 2, 3 and 7, an insulating blast tube 45 connects the passageway 23 in the support member 22 to a passageway 23' in the support member 22' of the middle interrupting unit 41. As shown in FIG. 7, a similar blast tube 46 connects the passageway 23 in the support member 22' to a similar passageway 23' in the end support member 22' at the left-hand of the arc-extinguishing assemblage 4. In this manner, all three interrupting units 41 are supplied with gas from the single high-pressure reservoir 9 under the control of the blast valve 24. Each one of the interrupting chambers 41 may be attached to the supporting member 22, or 22' by means of bolts, which extend through outwardly-extending lugs, or ears 47 (FIG. 6) on the interrupting chamber 41 and a flange portion 48 on the supporting member 22 or 22.

A relatively fixed contact assembly 51 and a movable contact 52 make contacting engagement within each interrupting chamber 41. The fixed contact assembly 51 comprises a cluster of contact finger members 53 formed integrally with a base 54, which is attached to the support member 22 by means of a bolt 55. The contact assembly 51 is generally cylindrical in shape, and the ends of the contact fingers 53 engage the movable contact 52 when it is in the closed-circuit position. The movable contact 52 is generally cylindrical in shape, and it extends through a close-fitting orifice opening 56 in the interrupting chamber 41. The outer end of the member 52 has a bifurcated portion which is attached to one of the cross-members 37 by means of a pin 58, as shown in FIG. 3. A rounded tip 59 is provided on the inner end of the movable contact 52. The tip 59 may be con1- posed of an arc-resistant material, such as copper-tungsten alloy. Likewise, the ends of the contact finger members 53 are tipped with an arc-resistant material. The main body portions of the contact fingers 53 and the contact member 52 may be composed of copper, or other good conducting material.

An arc-horn 61 is provided inside the interrupting chamber 41 exteriorly of the cluster of contact finger members 53, but in close proximity to one side of the cluster of fingers. The arc-horn 61 is attached to the support member 22 by means of a bolt 62. The arc-horn is tipped with an arc-resistant material, and the tip of the arc-horn 61 is adjacent to the vent opening 43 in the interrupting chamber 41. Since the arc-horn 61 is in close proximity to part of the contact fingers 53, the are created between the tip 59 of the movable contact member 52 and the contact fingers 53 when the contact members are opened, will transfer quickly to the archorn 61, as indicated by the are 63 in FIG. 5.

Also, since the arc-horn 61 is adjacent the vent opening 43, the are 63 will be blown toward the vent opening by the interrupting blast of gas, which flows transversely across the are 63, as shown by the arrows in FIG. 5. Since the arc-horn 61 is located exteriorly of the cluster of contact finger members 53, it does not interfere with the movable contact member 52 when it enters the cluster of fingers 53 during the closing operation.

In order to assist in guiding the longitudinal movement of the movable contact members 52, a guide cylinder 64 is provided for each one of the movable contacts 52. The left-hand end of each guide cylinder 64 is attached to one of the support members 22, or to the support casting 21, as shown in FIG. 2. The right-hand end of each guide cylinder 64 is sloted to provide a plurality of contact fingers 65, which slidably engage the respective movable contact 52. The guide cylinder 64 is also slotted, as at 66, to receive the cross-member 37, as shown in FIG. 3.

An electrostatic shield 67 may be provided around the contact fingers 65 to prevent a corona discharge from the fingers 65. The shield 67 may be attached to raised portions 68 on the cylinder 64. Compression springs 69 may be provided between the shield 67 and the fingers 65 to bias them toward the movable contact member 52. A guide ring 71 is provided at the end of the shield 67 to guide the movement of the movable contact 52. The guide ring 71 is preferably composed of polytetrafluoroethylene, generally known under the trade name Teflon, which has a low coefiicient of friction. Since the interrupting chamber 41 is also composed of Teflon, the friction between the interrupting chamber 41 and the movable contact 52 at the orifice opening 56 is also relatively low.

As explained hereinbefore, when the circuit breaker is tripped to release the operating mechanism, the accelerating pring 35 drives the operating rods 33 of the movable contact assembly 16 to the left, thereby simultaneously moving all of the movable contacts 52 lineally to the left. As previously explained, each movable contact 52 is connected to the operating rods 33 by means of one of the cross-members 37. In this manner the movable contact 52 in each one of the interrupting chambers 41 is separated from a fixed assembly of contact finger members 53 to establish an are 63 between the movable contact 52 and the contact fingers 53, as shown in FIG. 5. As also previously explained, the arc 63 is quickly transferred from the contact fingers 53 to the adjacently disposed arc-horn 61, as shown in FIG. 5.

The blast valve 24 is opened by the valve thrust lever 26, the pawl 27 and the operating lever 28 upon the initial movement of the contact members 52 toward the left. Thus, by the time the contact members 52, 53 have separated sufiiciently apart to create an are 63, the interrupting gas has entered each one of the interrupting chambers 41 from the high-pressure reservoir 9.

As shown by the arrows in FIG. 5, the interrupting gas is directed across the line of movement of the movable contact 52, and across the arc 63 to drive the are 63 toward the exhaust vent 43. In this manner the arc 63 is extinguished by the cross-blast action of the interrupting gas. The rib, or splitter 45 across the exhaust vent 43 will lengthen the are 63, thereby assisting in the interruption of the arc. Since a close fit is maintained around movable contact 52 at the orifice Opening 56, substantially all of the gas which enters the interrupting chamber 41 through the inlet opening 42 must leave the chamber through the exhaust vent 43. Therefore, the force of the high-pressure gas is utilized to blow the are 63 toward the exhaust vent 43. During the maximum instantaneous value of an alternating-current wave, the are 63 will be relatively short and unaffected by the gasblast. However, as the current wave approaches zero, the are 63 will be lengthened quickly by the gas flow, thereby producing a desirable peak of arc voltage just prior to interruption. In this manner the interrupting gas is utilized most effectively.

Since a plurality of interrupting breaks are provided for each pole-unit A, B or C of the circuit breaker 1, it is particularly suitable for utilization on relatively highvoltage power systems. Thus, the present structure retains all of the advantages of prior structures of the axial-flow type with respect to high-voltage service, and also obtains the advantages of cross-blast operation with respect to interrupting relatively high values of current. Therefore, the present structure is an improvement over prior circuit breakers of the gas-blast type.

In the modification shown in FIGS. 8, 9 and 10, the structure of the interrupting chamber 41' may be simplified, and the amount of material required for the interrupting chamber 41' may be reduced by providing a separate blast tube 44 to connect the interrupting chamber 41' with the passageway 23. As also shown in FIGS. 8 and 9, four segmental contact finger members 53 may be mounted in a generally cup-shaped contact retainer 72, which is attached to the support member 22 by a stud 73. One end of each of the contact fingers 53 is disposed in a groove 7- on the stud 73, and the other end engages the movable contact 52. A compression spring 75 may be provided between each contact finger 53 and the contact retainer 72 to bias the finger 53' inwardly towards the contact member 52.

As shown in FIGS. 8 and 9, the arc-horn 63. may be attached directly to one of the contact finger members 53'. This reduces the amount of space and the amount of material required for the arc-horn 61'. The interrupting chamber 41 may be attached to the support member 22 by means of lugs 47' in the manner hereinbefore described.

A maximum length for the are 63 may be obtained by providing an intermediate contact assembly 76, as shown in FIGS. 11, 12 and 13. The intermediate contact assembly 76 is disposed in the opening 80, through which the movable contact member 52 moves during the opening and closing operations of the interrupter. The intermediate contact assembly 76 comprises a generally cylindrical hollow member, the lower half 77 of which is solid, and part of the upper half of which is divided into a plurality of contact finger members 78 having a common base 79.

The lower half 77 is attached to the interrupting chamber 81, and the finger members 78 continuously bear against the movable contact member 52. An arc tip 82 is attached to the lower portion 77 of the contact assembly 76. Thus, the maximum length of the are 63 is determined by the distance between the arc tip 82 and the arc-horn 61.

FIG. 14 illustrates a modified-type of arc-chamber construction 91 involving a movable contact 52, which may be withdrawn from the orifice opening 56 to establish an axial flow of high-pressure gas thereto, as indicated by the arrows 93. It will be noted that not only is there present an axial flow of high-pressure gas issuing out of the orifice opening 56, but, additionally, transverse crossblast action is obtained by the utilization of the passage structure 42, 43. As a result, both the advantages of an axial flow and a transverse flow are achieved to result in rapid extinction of the established are 63.

With reference to FIG. 15 of the drawings, it will be noted that there is illustrated a modified-type of interrupting unit 95 involving a movable tubular venting, or ex hausting contact 93, which is cooperable with the relatively stationary contact structure 51, as previously described in connection with FIG. 3 of the drawings.

It will be noted that in accordance with the teachings of United States patent application filed Oct. 7, 1960, Ser. No. 61,284, by Robert G. Colclaser and Russell N. Yeclcley, that an axial flow of gas is ejected through the interior 100 of the movable tubular venting contact 98, to

carry the inner extremity of the arc 63a along the inner 6 Wall 98a of the movable tubular venting contact 98. Thus, not only is there provided an axial longitudinal blasting action of high-pressure gas through the interior 100 of the movable tubular venting contact 98, but, additionally, a desirable transverse cross-blasting of the.arc 63 is achieved by the use of the lateral exhaust port 43. Rapid arc extinction is, as a result, obtained.

From the foregoing description it is apparent that the invention provides a circuit interrupter having a crossblast action which can be utiiized in a circuit breaker of the dual-pressure gas type. The breaker is suitable for utilization on relatively high-voltage systems, and. is capable of interrupting relatively high values of current. The contact structures are of a rugged and lightweight construction capable of withstanding numerous interrupting operations.

Since numerous changes may be made in the abovedescribed construction, and different embodiments of the invention may be made without departing from the spirit and scope of the invention, it is intended that all the subject matter contained in the foregoing description, or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense.

We claim as our invention:

1. A gas-blast circuit interrupter including insulating means defining an arc-extinguishing unit, said unit defining an orifice opening and a laterally arranged exhaust vent, separable contact means including a movable tubular venting contact movable in said orifice opening to establish an are between said separable contacts, a highpressure gas reservoir chamber, a blast valve for controlling the flow of gas out of said high pressure gas reservoir chamber, said gas blast producing an axial flow of gas thrOugh the interior of the movable tubular venting contact to carry the extremity of the arc interiorly of the movable tubular venting contact, and a portion of said gas blast exhausting out said laterally arranged exhaust vent for addilional transverse cross-blasting of the are.

2. The combination of claim 1, wherein the separable contact means includes a stationary contact having an archorn (61) disposed adjacent one side of the laterally arranged exhaust vent.

3. In a dual-pressure type of circuit breaker, in combination, a tank containing an interrupting gas, a reservoir containing the same kind of gas at higher pressure than in the tank, a support member mounted inside the tank and having a passageway therethrough connecting with the reservoir, a blast valve controlling the flow of gas from the reservoir into the passageway, insulating means defining an arc extinguishing unit, said unit defining an "orifice opening and a laterally arranged exhaust vent, separable contact means including a movable tubular venting eontact movable in said orifice opening to establish an are between said separable contacts, opening of said blast valve producing an axial flow of gas through the interior of the movable tubular venting contact to carry the extremity of the are interiorly of the movable tubular venting contact, and a portion of said gas-blast exhausting out said laterally arranged exhaust vent for additional transverse cross-blasting of the arc.

References Cited UNITED STATES PATENTS 1,967,989 7/1934 Clerc 200-448 2,049,995 8/1936 Clerc 200148 2,422,784 6/1947 Jensen 200-148 2,757,261 7/1956 Lingal et a1. 200-148 3,099,733 7/1963 Ridings 200-145 3,160,727 12/1964 Colclaser et al 200148 3,291,949 12/1966 Crorner 200-148 FOREIGN PATENTS 65,962 12/ 1947 Denmark.

814,531 3/1937 France.

ROBERT S. MACON, Primary Examiner. 

